diff options
Diffstat (limited to 'Documentation/btrfs-select-super.asciidoc')
| -rw-r--r-- | Documentation/btrfs-select-super.asciidoc | 36 |
1 files changed, 27 insertions, 9 deletions
diff --git a/Documentation/btrfs-select-super.asciidoc b/Documentation/btrfs-select-super.asciidoc index a8d7ef00..6e94a034 100644 --- a/Documentation/btrfs-select-super.asciidoc +++ b/Documentation/btrfs-select-super.asciidoc @@ -3,27 +3,45 @@ btrfs-select-super(8) NAME ---- -btrfs-select-super - overwrite superblock with a backup +btrfs-select-super - overwrite primary superblock with a backup copy SYNOPSIS -------- -*btrfs-select-super* -s number dev +*btrfs-select-super* -s number <device> DESCRIPTION ----------- -*btrfs-select-super* destructively overwrites all copies of the superblock -with a specified copy. This helps with certain cases of damage, especially -when barriers were disabled during a power failure. You can find a valid -copy of the superblock with *btrfs check -s*. +Destructively overwrite all copies of the superblock +with a specified copy. This helps in certain cases, for example when write +barriers were disabled during a power failure and not all superblocks were +written, or if the primary superblock is damaged, eg. accidentally overwritten. -The filesystem specified by `dev` must not be mounted. +The filesystem specified by 'device' must not be mounted. + +NOTE: *Prior to overwriting the primary superblock, please make sure that the backup +copies are valid!* + +To dump a superblock use the *btrfs inspect-internal +dump-super* command, or the obsolete command *btrfs-show-super*. + +Then run the check (in the non-repair mode) using the command *btrfs check -s* +where '-s' specifies the superblock copy to use. + +Superblock copies exist in the following offsets on the device: + +- primary: '64KiB' (65536) +- 1st copy: '64MiB' (67108864) +- 2nd copy: '256GiB' (274877906944) + +A superblock size is '4KiB' (4096). OPTIONS ------- -s|--super <superblock>:: -use <superblock>th superblock copy, valid values are 0 up to 2 if the -respective superblock offset is within the filesystem +use 'superblock'th superblock copy, valid values are 0 1 or 2 if the +respective superblock offset is within the device size SEE ALSO -------- +`btrfs-inspect-internal`(8), `btrfsck check`(8) |